There are a number of conventional approaches to battery charging such as constant voltage charging method, constant current charging method, trickle charging method, and pulse charging method. These charging approaches vary in the charging speed, the impact on the battery life, the complexity of the circuit implementation, and the cost. It is discussed briefly as below.
The constant voltage charging method provides a constant voltage to charge the battery from the beginning to the end of charging. In the beginning of charging the battery, the charging voltage is greater than the battery voltage. The battery produces high current, so the sudden rise in temperature occurs in the battery. As the battery capacity increases, the battery voltage will be close to the voltage provided by the charger. At this situation, the charging time increases although the internal current of the battery is reduced.
Constant current charging method provided a constant and large current to charge the battery from the beginning to the end of charging. Although the charging time will be greatly reduced, the battery will produce a higher temperature, resulting in a lower battery life. If the battery is charged with a smaller constant current, the relative temperature is lower and the charging time is increased.
Trickle charge method is a two-stage charging, wherein a large current is applied to the battery in the beginning stage of charging and a small current is employed for charging in the last stage. This method can protect the battery and extends the battery life, but this method cannot determine whether the battery is fully charged.
In the pulse charging method, a constant current is initially applied to charge the battery, charging is then stopped temporarily for a period of time, and the charging continues with a constant current. This method can increase the battery charging efficiency because the charging is stopped temporarily for a period of time, and hence a maximum current that the battery can withstand is provided, and the charging time is reduced.
From the above discussion, the constant voltage charging method is simple in circuit design, but the charging speed is slow. The constant current charging method is simple in circuit implementation design and fast in charging, but the charge current is large and may damage the battery. The pulse charging method can reduce the charging time and extend the battery life, but the disadvantage is the high cost and the implementation is relatively difficult. Additionally, the constant current and constant voltage charging method is simple, but the charging speed is still slow.
Therefore, the conventional charging approaches vary in the charging speed, the impact on the battery life, the complexity of the circuit implementation, and the cost. It is desirable to have improvements on the charging method.